Spatial heterogeneities in structural temperature cause Kovacs’ expansion gap paradox in aging of glasses

Lulli, Matteo, Lee, Chun-Shing, Deng, Hai-Yao ORCID: https://orcid.org/0000-0001-6065-483X, Yip, Cho-Tung and Lam, Chi-Hang 2020. Spatial heterogeneities in structural temperature cause Kovacs’ expansion gap paradox in aging of glasses. Physical Review Letters 124 (9) , 095501. 10.1103/PhysRevLett.124.095501

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Abstract

Volume and enthalpy relaxation of glasses after a sudden temperature change has been extensively studied since Kovacs’ seminal work. One observes an asymmetric approach to equilibrium upon cooling versus heating and, more counterintuitively, the expansion gap paradox, i.e., a dependence on the initial temperature of the effective relaxation time even close to equilibrium when heating. Here, we show that a distinguishable-particle lattice model can capture both the asymmetry and the paradox. We quantitatively characterize the energetic states of the particle configurations using a physical realization of the fictive temperature called the structural temperature, which, in the heating case, displays a strong spatial heterogeneity. The system relaxes by nucleation and expansion of warmer mobile domains having attained the final temperature, against cooler immobile domains maintained at the initial temperature. A small population of these cooler regions persists close to equilibrium, thus explaining the paradox.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Publisher:	American Physical Society
ISSN:	0031-9007
Date of First Compliant Deposit:	9 March 2020
Date of Acceptance:	5 February 2020
Last Modified:	11 May 2023 12:02
URI:	https://orca.cardiff.ac.uk/id/eprint/130223

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